A thermoactuator is a driving part for advancing or retreating a rod on the basis of a temperature change. Such a thermoactuator is mounted on, e.g., a heat exchange device. The heat exchange device is known as, e.g., a waste heat recovery device. The thermoactuator mounted on the heat exchange device advances the rod when a temperature of a medium is high. The rod is forced to be retreated by an urging force of a return spring incorporated in the thermoactuator when the medium temperature decreases.
The waste heat recovery device has a heat recovery passage for recovery of heat of an exhaust gas, and a bypass passageway bypassing the heat recovery passage. A flow path for an exhaust gas is switched by a valve provided in the waste heat recovery device. To this valve is connected a thermoactuator. The valve is activated by activation of a rod of the thermoactuator. The thermoactuator is connected to a heat exchanger disposed in a heat recovery passage and activated by a temperature of a medium flowing through the heat exchanger.
The thermoactuator used in the manner discussed above is known from, for example, JP-A-2010-71454. The thermoactuator disclosed in JP-A-2010-71454 is shown in FIG. 20 hereof.
As shown in FIG. 20, a thermoactuator 200 includes a case 201 and a temperature-sensitive portion 210 attached to one end of the case 201 for sensing a temperature of surroundings of the case 201 (e.g., a medium temperature). The thermoactuator 200 also includes an actuator rod 203 received in a sleeve 212 of the temperature-sensitive portion 210 for advancing depending upon the temperature sensed by the temperature-sensitive portion 210. The thermoactuator 200 further includes a rod 204 disposed at a distal end of the actuator rod 203 for moving together with the rod in a left-rear direction of this figure. The thermoactuator 200 further includes a bearing 205 disposed on an outer circumference of a distal end of the rod 204 for guiding the rod 204, and a return spring 206 for urging the rod 204 in a direction to retreat the rod 204.
In the thermoactuator 200, a metal such as a steel material is used for the case 201. A resin such as polyimide is used for the bearing 205.
A wax 211 is accommodated in the temperature sensitive portion 210. When a temperature of the wax increases due to a high temperature of the surroundings of the temperature sensitive portion 210, the wax 211 expands. The expansion of the wax 211 forces the sleeve 212 to be compressed to advance the actuator rod 203.
When the temperature of the wax 211 decreases due to a low temperature of the surroundings of the temperature sensitive portion 210, the wax 211 shrinks. In this case, the rod 204 and the actuator rod 203 are forced to retreat under a force of the return spring 206.
The rod 204 is guided by the bearing 205 to move back and forth. As the rod 24 advances and retreats, the bearing 205 slightly wears away. The same goes for the sleeve 212 which the actuator rod 203 contacts. When an amount by which the bearing 205 or the sleeve 212 wears away reaches a predetermined amount, it is necessary to replace the bearing 205 or the sleeve 212.
It is necessary to reduce frequency of replacement of the bearing 205 or the sleeve 212 for use of the thermoactuator over a long period of time.